Electrical contact



March 15, 1932. B. w. JONES ETAL 1,849,837

ELECTRICAL CONTACT ,Filed Sept. 13. 1926 Clo'mzzwc-n Cadmium Alloy Inventors; Benjamin W. Jones, Charles F Ccw'pentem by M r P I Their Attorney Patented Mar. 15, 1932 UNITED STATES PATE T orrice I H BENJAMIN w. JONES m) enemas r; cnnrnnrnn, orscnnnncmnr, new roux, sssrenons r eminent ELECTRIC coumnr, A cozeronarxon or NEW Your:

nnncrnrcnr. course-r Application filed September 13, 1926. Serial No. 134,989.

This invention relates to electrical contacts, particularly contacts for electric switches.

The object of the invention is to provide an improved circuit making and breaking contact that has a substantial current-carrying capacity, as well as a relatively low and uniform contact resistance throughout a long period of circuit interrupting service.

The contact resistance encountered in the ordinary form of circuit controlling switch is an inherent characteristic that determines to a large degree the safe continuous currentcarrying capacity of the switch. This is particularly true in switches des gned for controlling heavy current circuits where the contact resistance and the resulting heating of the switch contacts readily may become the predominating factor controlling the maximum rating of the switch. In such switches copper is the material principally used for all current-carrying parts, as it has the lowest ohmic resistance, as well as the highest heat conductivity of any of the cheaper metals. However, switch contacts formed of copper soon become oxidized in service. Since the copper oxide is a very poor conductor of current, the contact resistance of the switch may be increased many times its initial value. The resulting heating of the switch contacts with normal current flow may become so excessive as to render the switch unsafe for continued service.

The difiiculties due to contact resistance are overcome in accordance with our present invention by forming the contacts of copper alloyed with cadmium. We have found that a small percentage of cadmium alloyed with the copper, as, for example,.10% of cadmium,

results in a material that has an initial contact resistance not materially greater than copper alone, and which will maintain the contact resistance at a fairly uniform. value over a long breaking service. As the contact is formed period of circuit making and of a homogeneous composition, the contact resistance characteristics are retained even though the initial contact surface is burned away or pitted by the arcing to which the switch contact is subjected.

As illustrating a preferredway in which the invention maybe carried into effect, we have shown in the accompanying drawing a switch contact of the usual type employed in heavy duty switches or contactors which is formed of an alloy comprising copper and cadmium in accordance with our invention.

The particular manner in which coppercadmium alloy is produced is not material to the present invention so long as a fairly homogeneous product is obtained, and any ordinary process of alloying the cadmium with the copper may be used. We, however, have found that the cadmium content of the alloy need not be more than substantially 10%, as contacts formed of alloys having a greater cadmium content than 10% are no better thanwith a smaller cadmium content.

The best results may be obtained with a switch contact formed of an alloy comprising substantially 99% of copper and 1% of cadmium. With contacts formed of an alloy of this constituency, the contact resistance remains substantially uniform at a relatively low value during long continued service in heavy current switches. Furthermore, the inevitable roughening of the surfaces of the switch contacts due to pitting and burning by the are necessarily occurring upon. establishing and interrupting the circuit do not materially vary the contact resistance of the contacts. This probably is due to the fact that under any conditions the actual contact is made only at relatively few points.

Due to the substantially uniform low contact resistance of our improved contacts, there is no-substantial heating localized at the contact surfaces even after the contact has been in service for a long period. This permits the current-carrying rating of an ordinary type of switch equipped with our improved contacts to be materially increased without exceeding permissible temperatures and in this way effects a material saving in providing 5 switches of the increased rating.

What we claim as new and desire to secure by Letters Patent of the United States, 1s,

A contact for electric switches'and the like 0 comprising an alloy .of copperandcadmium.

In Witness whereof, welhfl ehereunto set our hands this 11th day of September, 1926. v

BENJAMIN W. JONES. v 15 CHARLES F. CARPENTER. I a i 

